1. Field of Invention
The present invention relates to television receivers capable of receiving both analog and digital television signals.
2. Discussion of Related Art
Television signals are capable of being broadcast in different formats, such as a modulated analog format and a modulated digital format. Televisions may be designed to handle multiple formats. For example, television receivers within many televisions are capable of receiving radio frequency signals including both modulated analog television signals and modulated digital television signals. The television receiver is designed to process (e.g. filter, amplify and demodulate) both modulated analog television signals and modulated digital television signals.
A current approach for such a television receiver design will now be described with reference to FIG. 1. FIG. 1 depicts a television receiver 100 capable of processing (e.g. filtering, amplifying and demodulating) both modulated analog and modulated digital television signals. The receiver 100 accomplishes this by processing the modulated digital television signals and the modulated analog television signals separately. The receiver 100 includes a single tuner 110 with an Intermediate Frequency (IF) output 112 connected to two essentially separate signal paths: a digital demodulation signal path for digital 8-level Vestigial Sideband (8-VSB)/Quadrature Amplitude Modulation (QAM) reception and an analog demodulation signal path for analog video and audio reception. As depicted, the digital demodulation path includes one or two Surface Acoustic Wave (SAW) filters 120 coupled to the tuner 110, an Intermediate Frequency (IF) amplifier 130 coupled to the one or two SAW filters 120, and an 8-level Vestigial Sideband/Quadrature Amplitude Modulation (8-VSB/QAM) demodulator 140 coupled to the IF amplifier 130. The IF amplifier 130 is controlled by the 8-VSB/QAM demodulator 140 with an IF Automatic Gain Control (AGC) signal 116. As depicted, the analog demodulation path includes a video SAW filter 160 coupled to the tuner 110, an audio SAW filter 170 coupled to the tuner 110, a National Television System Committee (NTSC) demodulator 180 coupled to both the video SAW filter 160 and the audio SAW filter 170, and a stereo decoder 190 coupled to the NTSC demodulator. A Radio Frequency (RF) AGC switch 150 controls the tuner 110 with AGC signals 114 from both the 8-VSB/QAM demodulator 140 and the NTSC demodulator 180, thereby determining the tuner AGC characteristics depending on the specific channel reception requirements.